在運行MapReduce任務的時候如何避免這種情況!
100多個map任務,但是隻有1個reduce任務;
此時在mapred-site.xml中修改配置
<property><name>mapred.map.tasks</name><value>10</value><description>As a rule of thumb, use 10x the number of slaves(i.e., number of tasktrackers).
</description></property>
<property><name>mapred.reduce.tasks</name><value>2</value><description>As a rule of thumb, use 2x the number of slaveprocessors (i.e., number of tasktrackers).
</description></property>
map任務的個數建議設置爲slave*10(實際上無法控制,map任務的數量是輸入分片的數量), reduce任務的個數(分區的個數),建議設置爲2*salve